A radiator can crack due to corrosion, stress on the radiator, too much pressure on the radiator etc.
Rust can also destroy the metal in the Radiator causing a crack in the radiator.
A faulty Thermostat or a Leaking Head Gasket can cause Overheating or High Coolant Pressure inside the Radiator which can lead to a cracked radiator.
If you do not change your coolant enough, the radiator can start to corrode and crack over time.
You cannot operate a car with a cracked radiator, you should have it fixed right away, because the radiator will build up pressure when it is hot and the coolant will be pushed out very fast and the leaking holes will gradually get bigger and more coolant will come out of the radiator.
Too much pressure built up in the radiator can cause a radiator to explode or burst.
The pressure buildup in the radiator that causes the radiator to explode can be caused by a clog in the radiator, restriction, bad radiator cap, lime buildup etc.
The thermostat does not have to be changed when changing the radiator.
However if you're removing the hoses and replacing the radiator then it may be a good idea to replace the thermostat as well.
And if the radiator hoses are 10 years old or older it would be good to replace the radiator hoses at the same time you're replacing the radiator.
You can run a car or drive a car without a thermostat.
However if you run the car or drive the car without the thermostat then the engine won' reach it's operating temperature and the heater will usually not blow hot air.
If you drive without a thermostat, your engine will never reach its optimal operating temperature and your heater may blow cold air.
It happens because driving without a thermostat tricks your engine into thinking it is cold outside, causing it to adjust the gas mixing valve and push more fuel to the engine.
The thermostat opens and closes to keep the engine from overheating and to keep the engine at the proper operating temperature.
So it's best to have a thermostat in the engine although running the engine for a short amount of time without a thermostat if needed is okay.
Your car thermostat is an important part of your cooling system.
As the coolant gets hotter, the thermostat opens, allowing coolant to flow through to the radiator to be cooled.
The thermostat then opens and closes to keep the engine within a certain temperature range.
A engine thermostat is really cheap and worth the money to replace as it keeps your engine working properly and keeps your heater working as well.